Phytohormone Crosstalk Research: Cytokinin and its Crosstalk with Other Phytohormones

As signal molecules produced within the plant, phytohormones (plant hormones) control plant growth and development through the regulation of gene expression. They play also a crucial role in the regulation of cellular activities including elongation, cell division and differentiation, organogenesis, pattern formation, reproduction and responses to abiotic and biotic stress conditions. Cytokinins, auxins, gibberellins, abscisic acid and ethylene are five classic phytohormones that had been discovered by the middle of the twentieth century, while strigolactones, brassinosteroids, jasmonates and salicylates are of more recently characterized phytohormones. Interaction between different phytohormone pathways is essential in coordinating tissue outgrowth in response to environmental changes. In the past decades, hormone research has focused on elucidating signal transduction pathways from hormone perception to response. Such efforts have been well paid off by recent discoveries of almost all receptors for major classes of phytohormones. While receptors and pathways for individual hormones are being illustrated, growing evidence suggests that these signaling pathways are interconnected in a complex network. In these pathways, phytohormones not only coordinate fundamental developmental cues, but also convey environmental inputs by means of synergistic or antagonistic actions referred to as signaling crosstalk. Focusing on hormone action and crosstalk, this work suggested concentrating on phytohormones signaling, particularly cytokinin crosstalk with other hormones, in various plants. Plant responses to biotic and abiotic stresses are also elucidated regarding the dramatic recent progress in understanding the cytokinin-other phytohormones crosstalk. Keywords: Classic phytohormones, hormonal crosstalk, recent phytohormones.